The present invention relates to a magnetic disk unit and a floppy disk drive, and in particular to a magnetic head suitable to an apparatus for reading/writing information from/onto an information storage surface by using a plurality of magnetic heads.
A Magnetic head using a magnetoresistive film (hereafter abbreviated as MR head) has gradually come into use as a read head of magnetic memory units. The MR head uses a resistance change caused by magnetization of an extremely thin magnetoresistive film (MR film) such as a Permalloy* film. (* Permalloy is a trademark.) As the MR film, an extremely thin soft magnetic film usually having thickness of 1,000 .ANG. or less is used to raise its sensitivity. If the MR film is placed in a strong magnetic field, therefore, the MR film is completely magnetized and the resistance value of the MR film becomes constant. That is to say, so-called saturation is caused. Under such a state, its resistance value is not changed by an external magnetic field. If such an MR film is used in magnetic memory, its resistance value becomes constant irrespective of signal magnetic field generated by a recording medium. As a result, faithful signal reproduction cannot be performed.
On the other hand, there are magnetic disk units and floppy disk drives having disk-shaped recording media among magnetic memory units. In these memory units, information is recorded by using an identical recording clock as reference in both inner recording tracks and outer recording tracks of the disk. Accordingly, the recording density of outer recording tracks is lower than that of inner recording tracks. As a result, strong magnetization remains on outer recording tracks.
As MR heads used in such drives, an MR head integrated with a write head as described in JP-B-No. 59-35088 (published on Aug. 27, 1984, and corresponding to U.S. Ser. No. 498,504 filed on Aug. 19, 1974), and an MR head described in JP-A-No.59-121617 (laid open on July 13, 1984, and corresponding to U.S. Ser. No. 450,622 filed on Dec. 17, 1982) have been proposed, for example. In these known examples, however, the above described saturation of the MR film caused by a stronger signal magnetic field at outer tracks on the recording disk has not been considered at all.